The invention relates to a regulating system. In particular, this invention relates to an electrical regulating system including a splitter circuit.
An example of a regulating system of this type designed as a voltage regulator is described in EP 0 990 199 B1 and is briefly explained based on FIG. 1 to aid in understanding the following invention.
The voltage regulator includes an input terminal K10 for application of an input voltage Vin10 against a reference potential GND10, and an output terminal K20 for providing a regulated output voltage Vout dependent on a reference voltage Vref in order to supply load Z10.
Functioning as the actuating element of the regulating system is a bipolar transistor Q10, the collector-emitter path of which is connected between the input and output terminals K10, K20. The regulating signal is the base current Ib10 of the bipolar transistor, which current is provided by a current mirror arrangement which has a first and second current mirror path.
The first current mirror path includes a current mirror transistor Q20, connected as a diode, followed by a controlled current source in the form of a bipolar transistor Q40, which current source induces a current through a first current path which is dependent on reference signal Vref and on a voltage measurement signal, in turn dependent on the output voltage Vout, which signal is provided by a voltage divided R10, R20. For this purpose, the base of this bipolar transistor Q40 is driven by a comparison signal which provides a comparator 10 from reference signal Vref and the voltage measurement signal.
The second current mirror path includes a second current mirror transistor Q30, the base of which is connected to the base of the first current mirror transistor Q20, and the collector-emitter path of which forms the second current mirror path. This second current mirror path is connected to output terminal K20 through a diode.
In this regulating system, if the voltage Vec10 over the load path of the regulating transistor Q10 is below a predefined value Vth, produced by:Vth=Vbe10+Vcesat30+Vd10  (1),where Vbe10 is the base emitter voltage of the regulating transistor Q10, Vcesat30 is the saturation voltage of the second current mirror transistor Q30, and Vd10 is the conducting-state voltage of diode D1, then diode D1 is in the blocking state, and the regulating current Ib10 of the regulating transistor is supplied exclusively by the current source transistor Q40, then the applicable equation is:Ic40=Ib10=Iout/β10  (2),where Ic40 is the load current of current source transistor Q40, Iout10 is the load current flowing to the output terminal, and β10 is the current gain of regulating transistor Q10.
If the load path voltage Vec10 of regulating transistor Q10 exceeds the threshold value Vth according to (1), then diode D10 is conductive so that both current mirror paths contribute to regulating current Ib10. Based on the current mirror relationship set via the emitter surfaces of the two current mirror transistors, the applicable equation for current Ic40 through current mirror transistor Q40 is:Ic40=1/(M+1)·Ib10=Iout10/(β10·(M+1))  (3).
The analogous applicable equation for current Ic30 along the second current mirror path, which based on the current mirror relationship is proportional to current Ic40, is:Ic30=M/(M+1)·Ib10  (4)
With diode D10 conductive, regulating transistor Q10 and second current mirror transistor Q30 form a Darlington configuration, as a result of which the power loss for load path voltages Vec10 greater than Vth is significantly reduced, since only a small component of the regulating current remains unutilized, whereas a larger component (for M>1) is fed through diode D10 to output terminal K20.
A problematic aspect here is that when diode D10 is in the blocking state, the load current of current source transistor Q40 must increase by the factor M+1 relative to the conducting state of the diode in order to provide the required base current needed to drive regulating transistor Q10—which is equivalent to saying that the driving voltage Vb40 of this transistor, given by the equationVb40=Vb40+Ic40·R40  (5),must also increase by the factor M+1. R40 in (5) denotes the resistance value of the resistance following transistor Q40.
Frequently, however, this driving voltage is restricted by a protective circuit or by a supply voltage provided to driving circuit 10 with the risk that, given a small voltage drop, the regulator is not able to provide the full output current over the regulating transistor. Furthermore, problems due to a high substrate current may occur, if transistor Q40 is operated in his saturation region for high currents Ic40.
The goal of the invention is to provide a regulating system of the type referred to at the outset which, even in the event of a small voltage drop over the semiconductor element connected between the input and output terminals is able to provide the required output voltage, and which has a reduced power loss in the event of larger voltage drops.